Remove unneeded Auth Extension files

[damemi]

Now that the GCP auth extension is available in collector-contrib we don't need some of this code:

• Removes testdata/config.yaml and config_test.go (duplicated [upstream[(https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/extension/googleclientauthextension/config_test.go))
• Removes README steps about building into a custom collector
• Removes internal/metadata/status.go as it is duplicated upstream

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 62.34%. Comparing base (4caace7) to head (c600631).
Report is 11 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #842      +/-   ##
==========================================
+ Coverage   61.03%   62.34%   +1.30%     
==========================================
  Files          56       57       +1     
  Lines        5903     4894    -1009     
==========================================
- Hits         3603     3051     -552     
+ Misses       2143     1686     -457     
  Partials      157      157              

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